KR0131437B1 - Process for manufacturing high-strength bainitic steel rails with excellent rolling contact fatigue resistance - Google Patents

Abstract

High-strength bainitic steel rails with an excellent rolling-contact fatigue resistance containing 0.15% to 0.45% carbon, 0.15% to 2.00% silicon, 0.30% to 2.00% manganese, 0.50% to 3.00% chromium, and optionally at least one element selected from a group of molybdenum, nickel, nickel, copper, niobium, vanadium, titanium or boron is provided. The obtained rail exhibits a hardness of Hv 300 to 400 in the center of the rail head surface of the head and not lower than Hv 350 in the gage corner, and the hardness of the gage corner is higher than that of the center of the rail head surface by Hv 30 or more. <IMAGE>

Description

Baina art-based high strength rail with excellent rolling contact fatigue resistance and manufacturing method

Figure 1 shows the nominal part of the cross-sectional surface position of the rail head.

2 is a schematic diagram of a Nishihara style wear tester.

3 is a schematic diagram of a rolling contact fatigue tester.

4 is a schematic diagram of a tester for evaluating surface damage at the head of a bent rail.

* Explanation of symbols for main parts of the drawings

1: Rail head top face 2: Head corner part (gauge corner)

3: rail test piece 4: wheel test piece

5: gear 6: motor

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing high strength bainitic steel rails excellent in surface damage resistance of the head surface of a rail required in a high speed driving section of a passenger railway. High-strength rails having bainite structure that is resistant to fatigue damage in the corner corners or shelling or dark spot damage on the top of the head and does not cause such damage; and The manufacturing method is related.

In recent years, as a means of increasing the efficiency of rail transportation, an increase in the load capacity of trains and an increase in the speed of train operation have been made. Increasing the efficiency of such rail transportation means that the rail environment is used more severely, and therefore, further improvement of the rail material is required to cope with such a situation.

As a specific problem, the wear of the rails laid on the steep curved sections increases rapidly, and the fatigue damage occurring inside the rail gauge corner GC, which is the main contact position of the rails and the wheels, is frequently made.

As the countermeasure, the method shown below has been conventionally adopted. That is, (1) Unrolled alloy steel rail (refer to Unexamined-Japanese-Patent No. 50-140316) which added a large amount of alloying elements, such as (1) Cu and Mo.

(2) A heat treatment rail produced by accelerated cooling (gas injection cooling) of the rail head or the whole over a range of 700 to 550 ° C without adding an alloy (see Japanese Patent Application Laid-Open No. 55-23885).

(3) Low alloy heat-treated rails, which have a relatively low content of alloys, which improve not only wear resistance and damage resistance, but also lowering the hardness of welded parts (see Japanese Patent Publication No. 59-19173).

However, the characteristics of these rails are high-strength rails showing bainite, ferrite and fine pearlite structure, and their purpose is to improve wear resistance and to improve internal fatigue damage resistance.

On the other hand, in the rails of straight and gentle curve sections where wear or internal fatigue damage is not a problem, rolling-contact fatigue damage occurs on the rail head surface due to repeated contact of wheels and rails, resulting in peeling or It is sometimes seen that fatigue cracks created on the rail head surface diverge inside the rail head, causing row damage. This representative damage is a damage called "head squalling" or "dark spot" produced mainly in a straight line section of a high-speed railway such as a Shinkansen. However, in such a section, although the occurrence of such damage is remarkable, a rolled rail showing a conventional pearlite structure is used.

Rails in straight or gentle curved sections, mainly in passenger railways, produce rolling contact fatigue after a certain period of time (train tonnage) after the rail head surface. As a result of investigating the cause of the damage, the present inventors confirmed that the cause is that the fatigue damage layer caused by the repeated contact between the wheel and the rail accumulates in the rail head surface portion.

As a countermeasure, there is a method of grinding the surface of the rail head with a grinder on a regular basis, but there are problems in that the grinding car and its work cost are expensive, and that the grinding time cannot be sufficiently taken due to the train driving interval.

Another solution is to consider how to improve the wear rate of the rail head surface and to remove this fatigue layer by wear before fatigue damage accumulates. The wear characteristics of the rail are controlled by the hardness, and the hardness of the rail may be reduced to promote the wear. However, if the hardness is simply lowered, plastic deformation is generated in the rail head surface portion, which causes a lot of damage to the rail head surface such as cracking and peeling. Therefore, in the conventional rail showing the pearlite structure, it is difficult to prevent the occurrence of the damage.

Rail steels used so far have mainly a pearlite structure. This pearlite structure is a combination of low hardness ferrite structure and lamellar structure of plate-like hard cementite structure. On the track surface coming into contact with the wheel, a flexible ferrite structure is squeezed out, leaving only a hard cementite layer, and work hardening is applied to ensure the wear resistance required for the rail. However, at the same time, there has been a problem that a layered flow (metal flow) is generated in the track surface in the rail direction, and crack damage occurs accordingly.

On the other hand, in the bainite structure where the amount of abrasion is larger than that of the pearlite structure, since fine cementite is dispersed in the flexible ferrite structure matrix, the cementite together with the ferrite matrix is easily removed by wear during wheel driving, and the rail is accelerated by wear. The fatigue damage layer at the surface portion of can be removed. However, since the distribution of cementite described in Japanese Patent Application Laid-Open No. 50-14316, which is produced as it is, is low in alloy amount, the strength is lowered. For this reason, there existed a problem that the continuous flow of tissue (a chest flow) generate | occur | produces in the direction opposite to the train traveling direction on the rail head surface just below the wheel running surface, and a crack occurs according to this flow.

Moreover, as a method of solving this problem, it is also possible to add more alloys, such as Cr, and to manufacture bainite steel in which high strength is obtained even as it is rolled. However, high alloying not only greatly increases the unit cost of the rail steel, but also has a problem that a hard and fragile martensite structure is generated in the rail welded portion.

Thus, the present invention is to solve such problems, by adjusting the cooling conditions when the head of the rail is hot-rolled or reheated to a high temperature at the austenite temperature, the low alloy component system and high strength bay It is an object of the present invention to provide a high-strength rail excellent in rolling contact damage resistance at a low cost.

Another object of the present invention is to provide a low carbon bainite steel with appropriate hardness and wear resistance, thereby providing a high-strength rail with excellent rolling contact fatigue resistance without the occurrence of shelling or dark spot damage appearing in the gauge corner portion from the top of the head to the side surface. To provide.

Still another object of the present invention is a rolling contact having a hardness of Hv 300 to 400 of the top face of the rail head and a hardness of Hv 350 or more and a hardness of the gauge corner part of Hv30 or more higher than the hardness of the top face of the rail head. The present invention provides a high strength bainite rail having excellent fatigue resistance.

Further objects and features of the present invention will become apparent with reference to the following description and drawings.

This invention makes the summary the following structure in order to achieve the said objective. That is, (1) wt% contains C: 0.15 to 0.45%, Si: 0.15 to 2.00%, Mn: 0.30 to 2.00% Cr: 0.50 to 3.00%, or Mo: 0.10 to 0.60% as necessary. , Cu: 0.05-0.50%, Ni: 0.05-4.00%, the first group consisting of Ti: 0.01-0.05%, V: 0.03-0.30%, Nb: 0.01-0.05%, B: consisting of a third element consisting of 0.0005 to 0.0050%, containing at least one of each of these groups and elements, and hot rolling a steel consisting of iron and unavoidable impurities to obtain a rail And accelerated-cooling the head portion of the rail or the rail heated to a high temperature after hot rolling at an austenitic temperature from 1 to 10 ° C./sec from the austenitic temperature to a cooling stop temperature of 500 to 300 ° C., followed by a low temperature. Bainite-based high strength excellent in rolling contact fatigue resistance, comprising the step of naturally cooling to the region Method of manufacturing the rails.

(2) In the above (1), after the end of the accelerated cooling step, the rail head top surface is understood by reheating from the inside of the rail, and the temperature is raised to a maximum of 150 ° C. above the temperature at the end of the accelerated cooling. A method for producing a bainite-based high strength rail having excellent rolling contact fatigue resistance, which is naturally cooled to a low temperature range.

(3) A method for producing a bainite-based high strength rail excellent in rolling contact fatigue resistance as described in (2) above, wherein the temperature is raised to a maximum of 50 ° C above the temperature at the end of the accelerated cooling by reheating from the inside of the rail.

(4) The method for producing a bainite-based high strength rail excellent in rolling contact fatigue resistance according to the above (1), wherein the accelerated-cooled rail head portion is subsequently cooled to 1 to 40 ° C / min until near normal temperature.

Moreover, it is a rail manufactured from the steel containing the composition component of the said (1) description, Accelerated-cooling at 1-10 degreeC / sec between austenite area temperature and cooling stop temperature 500-300 degreeC, and it continues to normal temperature vicinity. It has a bainite structure obtained by cooling to the top, the hardness of the rail head top surface is Hv300 ~ 400, the hardness of the gauge corner part is Hv350 or more, and the hardness of the gauge corner part is Hv30 or more higher than the hardness of the rail head top surface. The high-strength bainite rail, which is excellent in rolling contact fatigue resistance, is also within the scope of the present invention. In the present specification, Hv means Vickers Hardness.

Hereinafter, the present invention will be described in detail.

In the present invention, first, the reason why the chemical component of the rail is defined as described above will be described.

C is an essential element for securing a certain hardness. If it is less than 0.15%, it is difficult to secure abrasion resistance as a rail steel, and if it is more than 0.45%, a lot of harmful pearlite structure is generated, or the bainite transformation rate is greatly reduced. In the recuperation process after the accelerated cooling, martensite structure harmful to the toughness of the rail is produced without completing the bainite transformation completely, so it is limited to 0.15 to 0.45%.

Si is an element that improves the strength by forming a solid solution in the ferrite matrix in the bainite structure, but the improvement in strength cannot be expected at 0.15% or less. In addition, if the content exceeds 2.00%, defects may easily occur on the surface during rolling of the rail, and island-like martensite structure is formed in the bainite structure to deteriorate the toughness of the rail, so it is limited to 0.15 to 2.00%.

Mn has the effect of increasing the hardenability of steel to make ferrite grains fine and improving its strength and toughness at the same time as C. However, Mn is less effective at less than 0.30% and harmful to surface quality if it exceeds 2.00%. Since many structures generate | occur | produce, it was limited to 0.30 to 2.00%.

Cr is an important element to secure the strength by finely dispersing cementite in bainite structure, but below 0.50%, the dispersion of cementite in bainite structure becomes rough, resulting in surface damage due to plastic deformation of the metal structure. Further, at 3.00% or more, not only coarsening of carbides occurs, but also the rate of bainite transformation is greatly reduced, and martensite structure harmful to the toughness of the rail without completely ending bainite transformation in the recuperation process after accelerated cooling. Is produced, so it is limited to 0.50 to 3.00%.

Moreover, the following element is added to the rail manufactured by the said component composition as needed, 1 type, or 2 or more types as needed. That is, the first group consisting of Mo: 0.10 to 0.60%, Cu: 0.05 to 0.50%, and Ni: 0.05 to 4.00% mainly contains Ti: 0.01 to 0.05% and V: 0.03 to The second group consisting of 0.30% and Nb: 0.01 to 0.05% is added mainly to improve the toughness of the steel, and B: 0.0005 to 0.0050% to more stably produce the bainite structure. Hereinafter, the reason why these chemical components were defined as above is demonstrated.

Mo is an indispensable element for strengthening stabilization of bainite structure and prevention of tempering embrittlement during welding, like Cr, but the effect is not sufficient at less than 0.10%, and if it exceeds 0.60%, the rate of bainite transformation Was significantly lowered, and was limited to 0.10 to 0.60% because martensite structure harmful to toughness was formed without completely finishing bainite transformation in the recuperation process after accelerated cooling.

Cu is an element which improves strength without compromising the toughness of steel. The effect was limited to 0.05 to 0.50% of range.

Ni is an element that stabilizes austenite particles, and has an effect of lowering bainite transformation temperature and miniaturizing bainite structure to increase strength and toughness, but at less than 0.05%, the effect is significantly small, and even if added more than 4.00% Since the improvement of the effect is not expected sufficiently, even if it adds 0.05-4.00% or more, since the improvement of the effect is not fully expected, it was limited to the range of 0.05-4.00%.

Ti contributes to the atomization of austenite grains during rolling heating of the rail by using the precipitated Ti (C, N) that does not dissolve even at high temperatures. However, at 0.01% or less, the effect is small. At 0.05% or more, coarsening of TiN occurs, which is a nucleus of fatigue damage inside the rail, which is harmful. Therefore, the effect is limited to 0.01 to 0.05%.

V can strengthen the bainite structure by the precipitation of V (C, N), but the effect is not sufficient below 0.03%, and the addition of V over 0.30% is due to the coarsening of V (C, N). Since embrittlement was generated, it was limited to 0.03 to 0.30%.

Nb is an austenite grain refining element, and the toughness and ductility of rail steel can be improved, but the effect is not sufficient at 0.01% or less, and at 0.05% or more, an Nb intermetallic compound is formed and causes embrittlement, so 0.01 to 0.05 It was limited to%.

B has an effect of suppressing formation of ferrite generated at the austenite grain boundary and is an effective element for stably producing bainite structure. However, at 0.0005% or less, the effect is weak. When 0,0050% or more is added, coarse compound of B is formed, and the rail material is deteriorated, so it is limited to 0.0005 to 0.0050%.

The rail composed of the above-described component composition is melted in a converter, an electric furnace, or other commonly used melting furnace, and is then made of a rail rolling material by ingot / fragmentation or continuous casting, and then hot rolling. It is molded into a predetermined shape via

In the present invention, the rail formed in this manner is used as the rail that retains the heat of high temperature in the austenite region after hot rolling, and if the rail is a lower temperature, the rail is heat treated in the austenite region. The head of the reheated rail is acceleratedly cooled to 1 to 10 ° C / sec between the austenitic temperature and the cooling stop temperature of 500 to 300 ° C.

And after completion | finish of accelerated cooling, a rail head part is further cooled to near normal temperature. The cooling at this time can employ | adopt natural cooling with reheating, or the cooling rate about 1-40 degree-C / min according to the objective. In the former case, a rail manufactured by using a temperature rise by reheating from the inside of the rail to 150 ° C. is first accelerated and cooled to start bainite transformation in a low temperature region, and then a minute bay by using a temperature rise by reheating afterwards. The knight tissue can be grown stably. In the latter case, bainite transformation is generated in the low temperature region, and fine and high-strength bainite structure can be stably produced by continuous cooling.

The reason why each of the acceleration cooling rates and the cooling crystalline temperature ranges are defined as described above is as follows.

First, the reason for limiting the accelerated cooling rate to the cooling stop temperature in the range of 1 to 10 ° C / sec is that bainite transformation occurs in the high temperature zone during cooling when cooling at a rate of less than 1 ° C / sec in the above component system. Initiation, coarse bainite tissue is produced. Therefore, since the strength of a rail falls and surface damage is caused, it is limited to 1 degree-C / sec or more. Moreover, when cooling at 10 degrees C / sec or more, large heat_generation | fever from the inside of a rail will generate | occur | produce in a subsequent reheating area | region, and coarse bainite structure will produce | generate. Therefore, since the intensity | strength of a rail falls and a surface damage is made good, it is limited to 10 degrees C / sec or less.

The reason why the accelerated cooling stop range at that time is limited to the range of 500 to 300 ° C from the austenite region temperature is that when the cooling is stopped at 500 ° C or higher, rough bainite structure in, for example, a recuperative region is changed depending on subsequent cooling conditions. This is easy to generate. Therefore, the strength of the rail is lowered and surface damage is caused, so it is limited to 500 ° C or less. In order to make finer bainite structure, it is preferable to set it as 450 degrees C or less. Moreover, when cooling to a low temperature below 300 degreeC, martensite structure will generate | occur | produce in bainite structure, and also the reheating inside a rail will not fully be obtained even if a reheating process is employ | adopted depending on subsequent cooling conditions, for example. And a lot of hard martensite tissue remains. Therefore, since the toughness of a rail falls remarkably, it limited to 300 degreeC or more. And in the steel of the component of this invention, Ms point is generally 350 degrees C or less. Therefore, in order to obtain stable bainite structure, it is preferable that the accelerated cooling stop temperature is 350 ° C or higher.

One of the cooling methods performed after the accelerated cooling stop temperature is natural cooling (cooling), which involves reheating.

In the present invention, the recuperation is limited to the natural recuperation from the inside of the rail, and no forced heating and cooling from the outside are performed. Thus, an experiment was conducted to accelerate the cooling of the head of the component rail of the present invention at a cooling rate of 1 to 10 ° C / sec at an austenite temperature and to stop the accelerated cooling at 400 to 300 ° C. The temperature rise by natural recuperation was confirmed in the range of -100 degreeC (in some cases, it may be close to 150 degreeC). In the above component system, the temperature range in which the fine bainite structure is transformed is in the range of 500 to 300 ° C. (preferably 350 ° C. or more), and after the recuperation after selecting the accelerated cooling rate and the accelerated cooling stop temperature, The temperature range becomes 500-350 degreeC, and is consistent with the temperature range in which high-strength bainite structure transforms.

On the other hand, if the temperature rises (reheating) about 100 ° C in this cooling stop temperature range, it is possible to secure the strength of the bainite steel, but some structures may coarsen due to the reheating, and thus the toughness decreases. Done. Therefore, the head of the component rail of the present invention is accelerated and cooled at a cooling rate of 1 to 10 ° C / sec at an austenite region temperature, and the accelerated cooling is stopped at a temperature range of 400 to 300 ° C. As a result of experiments for restraining heat recovery from heat recovery, coarsening of bainite structure is prevented when the temperature rise of the rail head portion due to reheating is 50 ° C. or less, and high strength and toughness bainite structure is produced. I could confirm that.

From these results, in the present invention, bainite transformation is started in a low temperature region by accelerating cooling at an austenite region temperature at 1 to 10 ° C / sec, and setting the accelerated cooling stop temperature to be in the range of 500 to 300 ° C, and then re-heating. It is possible to stably grow the fine bainite structure by using a temperature rise up to 150 ° C. or suppressing reheating by natural cooling including the above.

Moreover, this invention can also be achieved by carrying out controlled cooling of this cooling means in the range of 1-40 degreeC / min after this cooling stop temperature. That is, for example, in order to give a desired strength in a rail having a large cross section, it is desirable to perform controlled cooling such as cooling after the accelerated cooling stop temperature or slow cooling in the case of a small cross section. This is because fine cooling and high strength bainite structure can be obtained by such cooling. The cooling rate is limited in this way because when the cooling is less than 1 ° C / min, coarse carbides precipitate in the bainite structure, and the strength and toughness of the rail head are greatly reduced. This is because the bainite transformation is not completely completed, and martensite transformation occurs during this cooling, and a lot of hard martensite is generated in the bainite structure, which adversely affects the toughness of the rail.

And depending on the component system and the selection of the accelerated cooling rate, bainite transformation starts in the cooling stop temperature range of 500 to 300 ° C during the accelerated cooling, and when the transformation is completed in the subsequent recuperation region and immediately after the accelerated cooling. The bainite transformation starts after the recuperative region and may complete the transformation. However, in this cooling stop temperature range, any bainite structure is fine and does not have a great influence on the strength, toughness and damage resistance of the rail. As the bainite structure of the present invention, the cooling stop at 500 to 300 ° C. during the accelerated cooling degree. Both the bainite structure generated in the temperature range and the bainite structure generated in the recuperated region after accelerated cooling are included.

In addition, although the metal structure after this cooling is preferably a bainite structure, depending on the selection of the accelerated cooling rate and the cooling stop temperature, the fine martensite structure is mixed in the bainite structure, and finally, tempered by reheating inside the rail. It may exist as a martensite organization. However, even if a small amount of tempered martensite structure is incorporated in the bainite structure, since the rail strength, toughness, and manifestation resistance are not significantly influenced, a slight mixture of tempered martensite is used as the bainite rail structure. Also includes.

As a cooling medium at the time of accelerated cooling, gas-liquid mixtures, such as air or mist, are used, and cooling can be performed by spraying the said cooling medium with the nozzle arrange | positioned at the rail head both sides. By such a method, the hardness of the accelerated cooling and subsequent cooling of the rail is Hv 300 to 400 at the top of the rail head, Hv 350 or more at the corner of the rail head, and the strength of the head is preferably at least 1000 MPa. In this way, it is possible to manufacture a rail which prevents damage to the top surface of the rail head generated in a straight section, and at the same time prevents damage to the rail head corner surface generated in a train meander or a curved line section generated in a high speed railway.

The bainite rail produced by the method of the present invention as described above has surface damage resistance required as a high strength rail for high-speed passenger railway.

Hereinafter, embodiments of the present invention will be described. Figure 1 shows the nominal part of the head cross-sectional surface position of the JIS 60kg / m class rail used in the implementation, (1) is the rail head top, (2) is the corner portion of the head, (1), (2) The part containing the part is simply called the rail head.

Example 1

Table 1 shows the chemical components and cooling conditions of the steel of the present invention and the comparative steel. Table 2 shows the hardness of the steel and the comparative steel of the present invention, the results of measurement of the amount of wear after 500,000 iterations under the drying conditions in the Nishihara-type abrasion test, and the water-lubrication type using the disk test piece in which the shape of the rail and the wheel was scaled to 1/4. The surface damage occurrence life of a rolling contact fatigue test is shown. 2, the outline of the Nishihara-type abrasion tester is shown. In the figure, 3 denotes a rail test piece, 4 denotes a wheel test piece, 5 denotes a gear, and 6 denotes a motor. 3 shows an overview of the rolling contact fatigue tester. In the drawings, reference numeral 7 denotes a rail test piece, 8 a wheel test piece, 9 a motor, and 10 a bearing box.

The structure of the constituent material of the rail is as follows.

＊ Rail (10 pieces) of the present invention

Code | symbol A-J: The rail which shows the bainite structure manufactured by accelerating-cooling the rail head part and then naturally cooling it.

＊ Comparative rail (three)

Code K: A rail showing the bainite structure produced by accelerated cooling of the rail head and then naturally cooling.

Code L: Rail indicating naturally cooled bainite structure after rolling

Code M: Rail indicating naturally cooled perlite structure after rolling

In addition, test conditions were as follows.

＊ Wear test condition (common to all test rails)

-Tester: Nishihara Type Abrasion Tester

-Test piece shape: disc shaped test piece (outer diameter: 30mm, inner diameter: 16mm, thickness: 8mm)

-Test load: 490N

-Slip rate: 9%

-Relative Material: Tempered Martensitic Steel (Hv 350)

Atmosphere

Repeat count: 500,000 times

＊ Group contact fatigue test

-Tester: rolling contact fatigue tester

-Test piece shape: disc shape test piece

(Outer diameter: 200mm, cross section shape of rail test piece: 1/4 model of 60kg / m rail)

-Load test: 1.5 ton (radial load).

-Atmosphere: Drying + Water Lubrication (60㏄ / min)

-Number of revolutions: dry 100rpm, water lubrication 300rpm

-Number of repetitions: From 0 to 5000 times in dry state, then until damage occurs by water lubrication.

Note: The symbol Fe is used for both the surface damage resistant material component and the wear resistant material component.

Table 2 shows the hardness of the steel and the comparative steel of the present invention, the results of measurement of wear after 500,000 iterations under the drying conditions in the Nishihara-type abrasion test, and the water-producing cloud by the disk test specimens in which the shape of rails and wheels was scaled to 1/4. The surface damage occurrence life of a contact fatigue test is shown.

As is apparent from Table 2, the rails A, B, C, D, E and F, G, H, I, J of the present invention have a large amount of abrasion and rolling contact fatigue damage as compared to the rail M representing a conventional pearlite structure. The life span is greatly improved. Moreover, even if it compares with the rail L which shows the rail L and rail head part which show the bainite operation | rolling as it is rolling, and then naturally cool and manufactured the bainite structure, the rolling contact fatigue damage generation life improves significantly.

Example 2

Table 3 shows the chemical components and the cooling conditions of the steel and the comparative steel of the present invention. The rail steel and the comparative rail steel of the present invention manufactured as described above were scaled to 1/4 of the hardness of the head surface, abrasion measurement result after 500,000 repetitions under dry conditions in the Nishihara-type abrasion test, and the shape of the rail and the wheel to 1/4. Table 4 shows the surface damage generation life of the water-lubricated rolling contact fatigue test by the machined disk test specimen.

And the structure of the constituent material of code | symbol A-M, and the conditions of each test were employ | adopted the method similar to Example 1.

As is apparent from Table 4, the rails A to J of the present invention have a large amount of abrasion compared to the rail M representing the conventional pearlite structure, and the life of rolling contact fatigue damage is greatly improved. Moreover, the rolling contact fatigue damage generation life is greatly improved compared with the rail K which shows the rail K which shows the bainite structure as it is rolled, and the rail head part which heats and natural-cools after that, is produced.

Example 3

In Table 5, the chemical composition and cooling conditions of the rail of this invention and a comparative rail are shown.

4 shows a schematic diagram of a laboratory evaluation tester (Japanese Patent No. 11183162) for evaluating various surface damages of a rail head. The rail steel of this invention obtained by the process shown in Table 5 consists of all bainite structure, and as a comparative steel, (1) and (6) have bainite structure except that it is a pearlite structure rail.

Each of these rail steels is subjected to a laboratory evaluation test in which the wheel 12 rotates in contact with the head of the bending rail 11 shown in FIG. 4, and the surface is damaged under the wheel contact conditions corresponding to the curved section. Table 6 shows the test results for the generation life. Similarly, in Table 6, the test result which gave the contact condition of the wheel corresponding to a straight line section is also shown. In Fig. 4, reference numeral 11 denotes a bending rail, and reference numeral 12 denotes a wheel.

The laboratory evaluation test was carried out using the wheel used for the real Shinkansen by bending the rail which performed predetermined | prescribed heat processing to the inside of the head at 6m. The test condition is to reproduce the contact condition between the rail and the wheel, and to evaluate the damage generated on the surface of the corner part of the rail head by pressing the wheel flange to the corner part of the rail head as a reproduction of the contact condition of the curved section. In addition, as the straight section was reproduced, the top face of the rail and the center of the wheel were brought into contact with each other to evaluate the top face damage occurrence characteristics. In addition, the indication of the damage occurrence lifetime was represented by the cumulative passing tonnage of the train which is actually performed by a railroad.

From the above embodiment, by setting the hardness of the corner portion of the rail head portion to Hv400 or more, the damage occurrence life of the corner portion surface can be greatly improved compared to the comparative steel, and the hardness of the top surface of the rail head portion is controlled to Hv300 to 400. It is apparent that the occurrence of surface damage on the top face of the rail head can be suppressed.

Example 4

In Table 7, the chemical composition and cooling conditions of the rail of this invention and a comparative rail are shown.

Table 8 shows the hardness of the rail and the comparative rail of the present invention, the results of wear measurements after 500,000 repetitions under the drying conditions in the Nishihara-type abrasion test, and the number of the disk test pieces in which the shape of the rail and the wheel was scaled to 1/4. The surface damage occurrence life of the lubricated rolling contact fatigue test is shown. In addition, Table 9 shows the drop weight test results of the rail and the comparative rail of the present invention. In addition, in Table 8, the result (absorption energy value) of the impact test using the test piece collected from the rail head part was also written together.

The structure and test conditions of the constituent materials of the rails (A-J) and the comparative rails (K. L. M) of the present invention are the same as those in the first embodiment.

As is apparent from Table 8, the rails A to J of the present invention have a large amount of abrasion and greatly improve the life of rolling contact fatigue damage as compared to the rail M showing the conventional pearlite structure. Moreover, even if it is compared with the bainite rail K which rolled as it is, and the bainite rail L after rolling after accelerated cooling outside the conditions of this invention, and was naturally cooled, the life time of rolling contact fatigue damage improves significantly.

In Table 9, the results of the drop test of the rail and the comparative rail of the present invention are shown for the presence or absence of fracture after the drop test in all four test conditions, but the comparison rail is -30 to -50 deg. As for this fracture, it became clear that the rail of this invention does not fracture all four rails to -90 degreeC.

Claims (10)

A rail made of steel containing C: 0.15 to 0.45%, Si: 0.15 to 2.00%, Mn: 0.30 to 2.00%, Cr: 0.50 to 3.00%, and the balance being made of iron and unavoidable impurities. It has a bainite structure obtained by accelerating cooling from 1 to 10 ° C./sec from a knight station temperature to a cooling stop temperature of 500 to 300 ° C. and subsequently cooling the head of the rail to near room temperature. The hardness of the top surface of the rail head is Hv 300 to 400. The bainite high strength rail having excellent rolling contact fatigue resistance, wherein the gauge corner portion has a hardness of Hv350 or higher and the gauge corner portion has a hardness of Hv30 or higher than that of the rail head top surface. By weight, C: 0.15 to 0.45%, Si: 0.15 to 2.00%, Mn: 0.30 to 2.00%, Cr: 0.50 to 3.00%, Mo: 0.10 to 0.60%, Cu: 0.05 to 0.50%, A first group consisting of Ni: 0.05 to 4.00%, a second group consisting of Ti: 0.01 to 0.05%, V: 0.03 to 0.30%, Nb: 0.01 to 0.05%, and B: 0.0005 to 0.0050% A rail made of steel consisting of iron and unavoidable impurities, containing at least one member selected from the group, accelerated cooling from 1 to 10 ° C / sec from austenite temperature to 500-300 ° C It has a bainite structure obtained by cooling the head of the rail to the vicinity of room temperature, the hardness of the rail head top surface is Hv300-400, the hardness of the gauge corner part is Hv350 or more, and the hardness of the gauge corner part is Hv30 than the hardness of the rail head top surface. Bay with excellent rolling contact fatigue resistance, characterized by high hardness Knight high strength rail. By weight, it contains C: 0.15 to 0.45%, Si: 0.15 to 2.00%, Mn: 0.30 to 2.00%, Cr: 0.50 to 3.00%, and the balance is hot rolled to obtain a rail by steel rolling with iron and unavoidable impurities. Steps; Accelerating cooling the head of the rail or the rail heated to a high temperature after hot rolling at a temperature of 1 to 10 ° C / sec from the austenite temperature to the cooling stop temperature of 500 to 300 ° C; And a step of naturally cooling the head of the rail to a low temperature region. The method of manufacturing a bainite-based high strength rail excellent in rolling contact fatigue resistance, characterized by the above-mentioned. 4. The method of claim 3, wherein after the end of the accelerated cooling, the top surface of the rail head is raised to a maximum of 150 DEG C above the temperature at the end of the accelerated cooling by reheating from the inside of the rail, and then naturally cooled to the low temperature region. The manufacturing method of the bainite high strength rail which are used. The method for manufacturing a bainite-based high strength rail according to claim 4, wherein the temperature is raised to a maximum of 50 ° C from the temperature at the end of the accelerated cooling by reheating from the inside of the rail. The method for manufacturing a bainite-based high strength rail according to claim 3, wherein the accelerated-cooled rail head portion is subsequently cooled to 1 ° C to 40 ° C / min until near room temperature. By weight, C: 0.15 to 0.45%, Si: 0.15 to 2.00%, Mn: 0.30 to 2.00%, Cr: 0.50 to 3.00%, Mo: 0.10 to 0.60%, Cu: 0.05 to 0.50%, A first group consisting of Ni: 0.05 to 4.00%, a second group consisting of Ti: 0.01 to 0.05%, V: 0.03 to 0.30%, Nb: 0.01 to 0.05%, and B: 0.0005 to 0.0050% Hot rolling a steel comprising at least one selected from the group, the remainder being iron and inevitable impurities; Accelerating cooling the head of the rail or the rail heated to a high temperature after hot rolling at a temperature of 1 to 10 ° C / sec from the austenite temperature to the cooling stop temperature of 500 to 300 ° C; And a step of naturally cooling the head of the rail to a low temperature region. The method of manufacturing a bainite-based high strength rail excellent in rolling contact fatigue resistance, characterized by the above-mentioned. The method of claim 7, characterized in that after the end of the accelerated cooling, the top surface of the rail head is raised to a maximum of 150 ° C. above the temperature at the end of the accelerated cooling by reheating from the rail, and then naturally cooled to a low temperature zone. Method for producing bainite-based high strength rail. The method of manufacturing a bainite-based high strength rail according to claim 8, wherein the temperature is raised to a maximum of 50 ° C from the temperature at the end of the accelerated cooling by reheating from the inside of the rail. 8. The method for manufacturing a bainite-based high strength rail according to claim 7, wherein the accelerated-cooled rail head portion is subsequently cooled to 1 to 40 DEG C / min until near room temperature.